ATF dogs only eat when they successfully find what they are trained to seek, he said.

“The ATF trains all Labs,” Mr. Monday said. “They are hardy and friendly and we use food as a primary reward. The only time they eat is when they find explosives, and Labs love to eat.”

Mr. Monday explained the dogs are given small meals throughout the day during their training sessions, similar to how body-builders eat. They are weighed every Wednesday to make sure they don't gain or lose too much weight, he said.

“Their training sessions two to three times a day coincide with their meals,” he said. “You have to do that when training food-reward dogs.”

Other dogs used for searches that are not ATF-certified, such as German shepherds, have a lower food-drive, but very high play-drive, he said. With those types of dogs, handlers often use toy rewards such as tennis balls, he said.

Mr. Monday traveled up from Virginia to the former Fort Devens military base last week to conduct annual recertification trainings for ATF dogs and train 40 other dog-handler teams from around New England for the National Odor Recognition Test, known as NORT, on Thursday and Friday.

The NORT ensures non-ATF dogs used by state, local and federal law enforcement agencies can detect basic explosive odors, Mr. Monday said.

“We've offered the NORT test the last nine years to be proactive and make sure that police dogs used by agencies that support each other throughout the country are up to speed on finding explosives,” he said.

ATF officials at Devens also offered explosives training and discussed trends in explosives. Additionally, ATF chemists were on hand and the ATF's National Response Team vehicle that is deployed to investigate fires and explosions was available.

On Tuesday and Wednesday, the eight ATF canine-handler teams in New England went through recertification training. According to Debora A. Seifert, ATF spokeswoman, all but one of the ATF dogs in New England are located in Massachusetts. Two are assigned to Boston's police department, and a special agent handler and canine based in Boston is assigned to the ATF's Boston Field Division, which covers all of New England; one is assigned to North Andover's department; two to Everett's and one to New Bedford's. The other is assigned to East Hartford's department, she said.

Additionally, Ms. Seifert said, the canine handler from the Worcester Police Department attended the training in anticipation of the city getting its own bomb-sniffing dog with a $113,000 grant it was awarded.

There are only 32 ATF canine-handler teams in the country, Ms. Seifert said. Mr. Monday travels the country offering ATF recertification and NORT training, free of charge to all certified law enforcement officials, she said.

Everett Police officer and canine handler Christopher C. Hannon attended the ATF recertification at Devens with his partner, black Lab Hart. He and Hart were in Boston after the marathon bombings within an hour of getting called in, searching the scene after it was initially cleared to make sure there were no additional explosives, he said.

Officer Hannon said he went through a lengthy application process so the ATF could match him up with the right dog. Training an ATF dog is a year-round commitment, he said.

Hart is so well-disciplined, Officer Hannon said, that he will not attempt to steal food from the family's female boxer, Lea.

“She eats in a bowl and he'll sit there and watch and he will not eat it,” he said. “He doesn't understand eating that way.”

He demonstrated Hart's skills Thursday afternoon with 30 tins still set up in a circle from the NORT training earlier in the day — 10 containing explosive compounds and 20 containing distracter odors such as food, rubber bands, tape, batteries and other items.

Officer Hannon walked to each canister, put his hand inside and said, “Seek.” Hart stuck his snout inside each one and sniffed. Non-explosive odors gained little reaction from the dog, but when he detected an explosive compound, he would sit —ATF dogs' primary alert — and look up at Officer Hannon excitedly while waiting for his small food-reward for a job well done. Officer Hannon carries Hart's food in a pack strapped around his waist. While he gives Hart his reward, he also pats him and vocally responds with an elongated, “Good boy!” Then, Hart's ready to keep searching.

“He doesn't eat if he doesn't find anything,” he said. “It's rewarding with a dog. When he alerts you when he finds something and you see him get excited — you know the time you put in.”

Mr. Monday said all ATF dogs come from guide-dog foundations or the Puppies Behind Bars program, where prison inmates raise potential guide dogs, at around 17 to 19 months old.

“For some reason they don't make it through as guide dogs,” he said. “For the same reasons they don't succeed, we want them, like they are too curious, independent or like to sniff stuff a lot.”

For the first six weeks after the ATF procures a dog, it is introduced to explosives and “imprinted,” he said.

“They sniff explosives and we give them food,” he said. “When they get good at that, we teach them to sit when they find explosives.

“Sitting is a passive response. We don't want the dogs to disturb anything. We train them to sit immediately so they don't knock something over. That is different than some narcotic dogs that are trained to give aggressive responses like scratching and biting.”

The dogs are then taught how to conduct searches that progressively get harder and harder while the instructors introduce new explosives, Mr. Monday said, including fireworks compounds that can be used to make bombs.

“If we do it properly, our dogs can find over 19,000 different explosive compounds,” he said. “We train for all of them in the hopes that if it came to that, the dogs can find all of them.”

However, the biggest demand for ATF dogs is for the recovery of firearms and spent bullet shells, Mr. Monday said.

“We train our dogs to find spent shell casings and are very successful in firearm recovery,” he said. “A major part of canine training is to prevent violent crimes.”

Contact Paula Owen at powen@telegram.com. Follow her on Twitter @PaulaOwenTG.

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